Various air ventilation methods can be used to cool electric motors. One ventilation scheme, double-end-to-center or “X” ventilation, can bring inlet air from both ends of the motor and can exhaust air out of the center portion of the motor. The air is usually driven by two fans, one on each end of the motor, and by radial vents in the core itself. Another ventilation scheme, end-to-end or “Z” ventilation, can bring inlet air through one end of the motor and can exhaust air out of the opposite end of the motor. The air is usually driven by one large fan on the air outlet side of the motor, and by radial vents in the core itself. The air exiting the stator core can be collected along the back of the core and then can travels axially towards the air exhaust. Additionally, WPII (weather protected II) motors in the US market can have inlet and exhaust enclosures that meet special NEMA MG1 requirements.
Certain ventilation schemes can be more effective at particular motor speeds. For example, X ventilation usually provides better cooling than Z ventilation at higher speeds, and Z ventilation is usually more superior for cooling at lower speeds.
Because of the geometric differences between both ventilation types, one scheme is typically selected for a particular motor product line and manufactured and specified for use for all speeds, resulting in motors with optimized cooling at certain speeds only. As a result, different motor product lines can comprise different ventilation systems, which can be costly and inefficient.